DataGuard & RAC are two most important topic for Oracle DBAs & Apps DBA’s managing EBS R12, and both these are still applicable in Cloud (in fact more important now)

In this post, We are going to look at High Availability (HA) and Disaster Recovery (DR) on Cloud and I’ll be focusing on Standby Databases also known as DataGuard. The same is covered in the 60 mins Live Show I did on Facebook.

Note: First let’s look at basic concepts related to RAC or Extended RAC & for DR Standby/DataGuard: Three Types. If you know this all then scroll down at the end, for points specific to HA & DR in Oracle Cloud.

High Availability (RAC)

High Availability (HA) stands for Active-Active where clients can connect to more than one node. It helps in Scalability(can serve more clients and better response time) and avoid a single point of Failover.

RAC stands for Real Application Cluster that provides HA for Database Tier (as shown in the bottom layer of the picture below). For Application Tier, you configure multiple app/web servers (as shown in top layer of picture below)

If you don’t have the time to look at the entire 60 mins video, but still want to know about HA: Active-Active, you can start from 17 min25 sec.

In RAC you will have multiple machines each running database instance(memory & database processes) but all instances talking to a single database on a cluster file system (data files where data is stored).

In RAC, Session Replication between nodes occurs so that the data in Instance 1 can be accessed by data in the memory of Instance 2 and so on using private interconnect. Check all networking requirements HERE.

RAC provides HA within datacenter but doesn’t provide failure against entire datacenter. Extended/Stretched RAC is an option for extending RAC across the datacenter. Get more information on stretched cluster HERE.

Disaster Recovery (DataGuard)

RAC license could be costly and doesn’t cover failure against entire datacenter and you still want a Disaster Recovery (DR) solution and that’s where Standby Database (aka Dataguard) comes into the picture.

Standby Database (DataGuard) is a process of setting up two databases which might be geographically distant where one database acts as Primary (open in Read/Write and serving clients) while another as Standby (accepting changes from primary and possibly applying them to stay in sync).

The Primary Database sends a Redo Logs to Standby, that is then applied to standby database (based on type Standby Database). In the Live 60 minutes show, I discussed three different types of Standby Database (Dataguard Configuration) i.e. Physical, Logical and Snapshot.

Note: Failover from Primary Database to Standby Database, can be Manual or Automatic (using Observer process in Fast Start Failover).

DataGuard Vs Active DataGuard

Unlike in DataGuard, you can open the Standby Database in Active DataGuard in Read Only mode for reporting purpose.

HA & DR in Cloud

If you are deploying RAC or DataGuard on Oracle Public Cloud then you must select correct Software Edition & Database Type while creating Database on Oracle Cloud.